How much sample do I need for a carbon?

Probably the most common question I get asked is "How much sample do I need for a carbon?" The answer is - it depends on the probe being used, the molecular weight of the compound, and how long you are prepared to run the experiment for. For most people, however, "it depends" is not a very satisfactory answer, so I've tried to find a way to get some numbers to answer the question.

The impact of poor tuning and matching

Tuning and matching is the process of optimising the frequency and resistance of the circuit that includes the detection coil. Every sample has a slightly different ionic content and so the probe should be tuned and matched for each sample. Modern NMR probes have automatic tuning and matching devices, but the Skaggs NMR Facility probes do not. Here, I look at the impact of poor tuning and matching on a 1D ¹H spectrum.

Altmetrics and citations

Publications arising from work at the SSPPS NMR Facility are tracked on the Facility's Publications webpage. Along with breakdowns of the list by year, lab and journal, this page also reports the Altmetric score for each publication. This is a measure of the attention the article has received, predominantly on social media. To see how the Altmetric score compares with citations I prepared a few graphs.

The acquisition time

In an NMR experiment the acquisition time is the period used to record the signal. Changing this value can affect the quality and appearance of your spectrum. Typically, larger acquisition times are used for one-dimensional spectra, with shorter values used in multidimensional spectra. The impact of using different acquisition times on 1D ¹H spectra are shown in this post.

The relaxation delay

The relaxation delay is one of the basic NMR parameters. Optimising the relaxation delay can help improve the appearance of your spectra and increase the accuracy of your integrals. In this post its impact on 1D ¹H spectra is shown.

Fill volume for 1.7mm NMR tubes

The SSPPS NMR Facility routinely uses a 1.7mm micro-cryoprobe that takes capillary NMR tubes with a diameter of 1.7mm instead of the standard 5mm NMR tubes. These capillary tubes require much less sample volume than a standard tube, but exactly how much should be used? And what happens if there is too little? Or too much?

Fluorine and phosphorus heteronuclear coupling

The most commonly encountered coupling in NMR spectra is due to ¹H, but other nuclei can induce splitting of signals as well. The previous post discussed how coupling to ¹³C at natural abundance produces the small ¹³C satellite peaks. The other heteronuclear couplings that are most likely to be observed are due to ¹⁹F and ³¹P. Examples of these in 1D ¹H and  ¹³C spectra are shown below.